1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal device having patterned spacers and a method of fabricating the same.
2. Discussion of the Related Art
In general, a liquid crystal display (LCD) device makes use of optical anisotropy and polarization properties of liquid crystal molecules. The liquid crystal molecules have a definite orientational alignment that results from their long thin shape. The orientation of the liquid crystal molecules can be controlled by applying an electric field to the liquid crystal molecules. The orientation of the liquid crystal molecules changes in accordance with an intensity of the applied electric field. Incident light through a liquid crystal material is refracted due to an orientation of the liquid crystal molecules. Thus, an intensity of the incident light can be controlled and images can be displayed.
Among the various types of LCD devices commonly used, active matrix LCD (AM-LCD) devices have been developed because of their high resolution and superior display of moving images. In an active matrix LCD (AM-LCD) device, thin film transistors (TFTs) and pixel electrodes connected to the TFTs are disposed in a matrix configuration.
The LCD device includes upper and lower substrates, and a liquid crystal layer interposed therebetween. The upper substrate and lower substrate are commonly referred to as a color filter substrate and an array substrate, respectively. A common electrode and color filter layers are formed on the upper substrate. TFTs and pixel electrodes are formed on the lower substrate.
After forming the common electrode, the color filter layers, the TFTs and the pixel electrodes, the LCD device undergoes a liquid crystal cell process where a liquid crystal layer is formed between the upper and lower substrates. The liquid crystal cell process may be divided into a process of forming an alignment layer to align the liquid crystal molecules, a process of forming a cell gap, a process of attaching the color filter and array substrates together, a process of cutting the attached color filter and array substrates into cells, and a process of injecting the liquid crystal molecules. Accordingly, a liquid crystal display panel is fabricated using the liquid crystal cell process.
FIG. 1 is a schematic cross sectional view of a liquid crystal display device according to the related art. Referring to FIG. 1, a liquid crystal device includes upper and lower substrates 41 and 21 spaced apart from each other, and a liquid crystal layer 50 interposed therebetween. A gate line (not shown) and a data line (not shown) crossing the gate line are formed along an inner surface of the lower substrate 21, wherein a pixel region “P” is defined by crossings of the gate and data lines. A thin film transistor “Tr” is formed at the crossing portion of the gate and data lines. A pixel electrode 35 is formed in the pixel region “P” and is connected to the thin film transistor “Tr.” The lower substrate 21, the gate and data lines, and the pixel electrode 35 constitute an array substrate 20. A black matrix 43 is formed along an inner surface of the upper substrate 41 in a boundary region of the pixel region “P” in order to prevent light leakage and to shield the thin film transistor “Tr” from incident light.
A color filter layer 45 includes red, green and blue filters 45a, 45b and 45con the black matrix 43 in order to filter light having specific wavelengths. A common electrode 47 is formed on the color filter layer 45. Although not shown, each of red, green and blue sub-color filter 45a, 45b and 45c are located in each of the pixel regions “P,” respectively. The upper substrate 41, the black matrix 43, the color filter layer 45 and the common layer 47 constitute a color filter substrate 40. In addition, the liquid crystal layer 50 is formed between the pixel electrode 35 and the common electrode 47, wherein an electric field is applied across the liquid crystal layer 50 through the pixel electrode 35 and the common electrode 47.
Ball spacers 52 are disposed between the pixel electrode 35 and the common electrode 47 to maintain the uniform cell gap along with a seal pattern (not shown). Although not shown, upper and lower alignment layers may be formed on the common electrode 47 and the pixel electrode 35, respectively, to align the liquid crystal molecules. Specifically, the ball spacers 52 may be made of an elastic material deformable under an applied external pressure. For example, the ball spacers 52 may be made of a glass fiber or an organic material. However, since the ball spacers 52 are randomly distributed between the upper and lower substrates 41 and 21, the quality of an alignment layer may be lowered due to movement of the ball spacers 52. In addition, light leakage may occur within regions adjacent to the ball spacers 52 due to an adsorption force between the liquid crystal molecules adjacent to the ball spacers 52. Moreover, a uniform cell gap may not be obtained in a large sized LCD device. Furthermore, since the ball spacers 52 are elastic and do not remain at a fixed position, a severe ripple phenomenon may occur when the LCD device is touched. Thus, superior display quality can not be obtained in the LCD device using the ball spacers 52 to maintain a uniform cell gap.
On the other hand, a uniform cell gap may be easily obtained using the patterned spacers since they are formed in a non-pixel region, thereby preventing light leakage and improving contrast ratio. In addition, the patterned spacers may be applied to an LCD device requiring a small cell gap due to precise control of the cell gap. Furthermore, since the patterned spacers are fixed, they may be easily applied to large sized LCD devices and the ripple phenomenon may be prevented when the LCD device is touched. Since the patterned spacers may be formed directly on the overcoat layer in an IPS-mode LCD device, reliability of the patterned spacers is improved.
FIGS. 2A to 2E are schematic cross sectional views of a substrate during a process for fabricating a color filter substrate of a liquid crystal display device according to the related art. Referring to FIG. 2A, a black matrix 63 having first to third sub-open portions 65a, 65b and 65c is formed on a substrate 60 in which the pixel regions “P” shown in FIG. 1 are defined. Each of the first to third sub-open portions 65a, 65b and 65c correspond to each of the pixel regions “P.”
Referring to FIG. 2B, a red filter 66a is formed in the first sub-open portion 65a of the black matrix 63. Although not shown, the red color filter 66a may be formed through photolithographic processes using a negative-type color pigment, wherein a portion of the negative-type color pigment is exposed through a mask and remains as a pattern after a subsequent development step. Although not shown, the black matrix 63 is disposed in a periphery of each sub-color filter 65a, 65b or 65c as a single body in plan view.
Referring to FIG. 2C, green and blue filters 66b and 66c are sequentially formed in the second and third sub-open portions 65b and 65c of the black matrix 63, respectively. The green and blue filters 66b and 66c are formed using the same method adapted for the red filter 66a. The red, green and blue filters 66a, 66b and 66c constitute a color filter layer 66.
Referring to FIG. 2D, an overcoat layer 69, such as an organic material having excellent planarization properties, is formed on the color filter layer 66. Referring to FIG. 2E, a plurality of patterned spacers 72 having a pillar shape are formed on the overcoat layer 69 corresponding to the portion of the black matrix 63.
The process of forming color filter substrate having these patterned spacers 72 is completed through total five mask processes including the step of forming the black matrix 63, the step of forming the red sub-color filter 66a, the step of forming the green sub-color filter 66b, the step of forming the blue sub-color filter 66c, the step of forming the overcoat layer 69, and the step of forming the patterned spacer 72.
In the mask process for the color filter substrate of the liquid crystal display device according to the related art, a mask is very expensive. In addition, since the production cost is proportional to the number of masks, a large number of masks increases the production cost for forming the color filter substrate.